Messages in this thread | | | Subject | Re: /sys/block [was: [PATCH 007 of 7] md: Get name for block device in sysfs] | From | Kay Sievers <> | Date | Mon, 17 Dec 2007 09:24:39 +0100 |
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On Mon, 2007-12-17 at 08:29 +0300, Michael Tokarev wrote: > Kay Sievers wrote: > > On Mon, 2007-12-17 at 09:43 +1100, Neil Brown wrote: > >> On Saturday December 15, kay.sievers@vrfy.org wrote: > >>> On Dec 14, 2007 7:26 AM, NeilBrown <neilb@suse.de> wrote: > >>>> Given an fd on a block device, returns a string like > >>>> > >>>> /block/sda/sda1 > >>>> > >>>> which can be used to find related information in /sys. > >> .... > >>> As pointed out to when you came up with the idea, we can't do this. A devpath > >>> is a path to the device and will not necessarily start with "/block" for block > >>> devices. It may start with "/devices" and can be much longer than > >>> BDEVNAME_SIZE*2 + 10. > >> When you say "will not necessarily" can I take that to mean that it > >> currently does, but it might (will) change?? > > > > It's in -mm. The devpath for all block devices, like for all other > > devices, will start with /devices/* if !SYSFS_DEPRECATED. > > This is the second time I come across this (planned?) change, and for > the second time I can't understand it. > > How to distinguish char devices from block devices in sysfs? > Is the only way to read a symlink `subsystem' in the device > directory?
By its subsystem value (block), from the symlink, from the environment, or from $1.
> For now, I've a shell code (used heavily in numerous places), > which looks like this: > > function makedev() { > ... > case $DEVPATH in > /block/*) TYPE=b ;; > *) TYPE=c ;; > esac > ... > mknod /dev/$DEV $TYPE $MAJOR $MINOR > } > > The only external process invocation in there is mknod, all > the rest is done using pure shell constructs. Is it really > necessary to spawn another process just to read a symlink > now? It will be almost 2 times slower....
No need.
> (Sure thing this may be rewritten in C, but using shell it's > MUCH easier to customize if necessary.)
$SUBSYSTEM == "block"
> Also, /sys/block/ directory is very easy to use currently, -- > unlike other /sys/ stuff which is way too deep and often > placed in unknown/unexpected places (and /sys/class/ and > /sys/bus/ directories are changing all the time).
/sys/block is still there and contains symlinks. And all this happens only for !SYSFS_DEPRECATED.
> What's the benefit of moving things from /sys/block/ to > /sys/devices/ ?
Unification. Block devices are "struct devices", use a class, use the common driver core code instead of their own, show up in the tree, and can be parents for other devices.
Kay
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